Hello all,

I have a Rheem furnace (model # RGLA-07EC-ER, serial # F4790 0817) with an igniter and it is acting up (now that has gotten cold of course). It will kick on the ignitier, light the flame, and then turn the gas on to full mode and then it shuts the gas off between 1 and roughly 15 secs later, usually before the fan even kicks in. Then it waits a short period and does it again, over and over (I assume there is a time delay in the ignition electronics).

Looking at the wiring diagram, it appears to have two over-temp switches, the fan door switch, and some other switch (not named and labeled as optional) on what I call the "heater on" line that initiates the ignition electronics.

I believe the fan door switch is working correctly, so it has to be the over-temp switches or the unknown switch. I noticed that the wire feeding the ignition system comes out of the fan limit box, so maybe that is the unknown switch?

What typically causes this repeated cycle of flaming on and then shutting it off immediately after? Are the over-temp sensors known to become too sensitive to heat (and therefore open the circuit at lower temps) or is it possibly something in my fan limit control box that is causing this? This is an older furnace, manufactured in the early 90's I believe.

Thank you in advance!

Matt

Try cleaning the flame sensor with steel wool or sand paper. It is the cheapest thing to try first.

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